Various buzzer structures, adapted to be energized by AC and/or DC, are in themselves well known. Such buzzer structures typically comprise a coil unit associated with a vibratory armature mounted adjacent thereto. In the case of AC operation, the armature may constitute a permanent magnet adapted to be successively attracted to and repelled by the changing polarity poles produced in the AC energized coil unit or, if the armature has a comparatively small mass, the armature may comprise a strip of magnetic metal mounted on a spring and adapted to be successively attracted to one end of the coil unit at a frequency dependent upon the frequency of energization, e.g., a 60-cycle coil energization causes armature vibration at 120 cycles per second. In the case of DC operation, the armature is further associated with a contact pair which controls the energization circuit of the coil in well known fashion to successively make and break said energization circuit and thereby cause vibratory motion of the armature. The present invention is concerned, in general, with buzzers of these various different types.
In buzzer assemblies of the general types described above, proper operation of the buzzer depends, inter alia, on proper positioning of the coil unit and armature relative to one another, i.e., if the gap between these elements is too large the armature will not be attracted to the coil unit when the coil unit is energized. It is possible, of course to calculate precisely where the parts should be positioned relative to one another in dependence upon the parameters of the coil unit and armature and the operating conditons which are desired, and to carefully engineer and assemble the buzzer based upon such calculations. However an approach of this type, and the resultant precision in manufacture and assembly which it contemplates, is not economically justifiable when it is desired to provide a simple, comparatively inexpensive buzzer assembly; and in this latter case, the usual practice has been to mount the coil unit and armature in general proximity to one another within a housing, and then to manually adjust the positions of these elements relative to one another while observing the operating state of the buzzer thereby to establish the operating point of the buzzer. More particularly, it has been the practice heretofore to provide an adjustable set screw in the buzzer housing positioned to bear upon a portion of the coil unit and, with the coil energized but with the gap between the coil unit and armature too large to cause the armature to be attracted to the energized coil unit, to turn the set screw thereby to force the coil unit toward the armature until the gap has been reduced sufficiently to cause the buzzer to commence its operation, at which time the set screw is locked into place.
The prior art adjustment technique discussed above has a number of disadvantages. It requires, of course, the provision of a set screw and associated tapped hole in the housing which tend to increase the cost of the buzzer somewhat; and while the cost of these items is comparatively small, it may become significant in the case of an extremely inexpensive buzzer construction. In addition, the adjustment procedure, requiring the turning down of the set screw and the subsequent locking thereof into place, is comparatively slow and does not lend itself to an automated procedure. Moreover, the adjustment may not be as permanent as desired since there is always the possibility that an improperly locked screw may shake loose, in which event the dimensions of the gap between the coil unit and armature can change to render the buzzer inoperative.
The present invention obviates all of these disadvantages of the prior art.